Biological reactors or bioreactors have been widely used to biologically degrade contaminants such as biological-consumable organic or inorganic substances in municipal and industrial wastewaters in treatment systems. Typically, there are two types of biological reactors commercially used: i) activated sludge reactors, and ii) biofilm reactors. Conventional designs for biological wastewater treatment systems using conventional activated sludge and biofilm reactors require a unit for sludge or particle separation to remove some suspended solid in the effluents from the reactors before the effluents are discharged to natural water reservoirs. The capital cost for the wastewater treatment systems and also operating costs such as electricity consumption and chemical use would be reduced if the particle separation unit was not required.
Periodic maintenance of conventional biological wastewater treatment systems results in additional cost and loss in clean effluent productivity. Moreover, aerobic biological reactors of activated sludge and biofilm for wastewater treatment systems necessitate extra management for sludge disposals and thus incur additional costs for the sludge handling system. The excess sludge from the aerobic biological reactors of the background art is required to be properly managed and adequately disposed of.
High suspended solid concentrations in the effluents, high viscosities in the effluents, and excess sludge management in the conventional aerobic activated sludge biological reactors cause operational difficulties and incur extra capital costs of overall wastewater treatment systems and clean water production systems.
The present invention is arranged for handling at least some of the problems resulting from high suspended solid and excess aerobic sludge production in the feedwater treatment systems and thus to significantly reduce the costs of operation and maintenance in biological feedwater treatment systems.
The present invention provides a novel biological reactor designed to control the suspended solid in the reactor, to reduce amount of excess aerobic sludge produced from aerobic digestion, and to produce an effluent having a relatively low concentration of suspended solids.
General Biological Background
The composition of the wastewater may vary from one wastewater producing society to another, and depends on the water quality, the use and conservational practices, cultural attributes, industrial activity and kinds of industrial treatment executed on site. One problem caused by spilling raw wastewater to a recipient is eutrophication of the recipient due to the introduction of nutritional substances (nitrogen, phosphorus and organic matter) which are limiting factors for biological growth. Spilling raw wastewater to the environment incurs the risk of spreading of pathogenic organisms and accumulation and storage of various heavy metals. Biological reactors are used to biodegrade organic or inorganic substances in municipal and industrial wastewaters in treatment systems.
Anaerobic/anoxic wastewater treatment is the biological treatment of wastewater generally without supplying air or elemental Oxygen. The organic compounds of the wastewater may be converted by anaerobic/anoxic micro organisms and produce gas containing a large proportion of methane and some carbon dioxide, known as biogas.
Denitrification takes place in an anaerobic/anoxic environment by anaerobic/anoxic bacteria. The denitrification process in an anoxic environment may convert Nitrite/Nitrate to Nitrogen gas which is generally harmless if released to the atmosphere. Nitrate, which may be undesired in the effluent and readily leached to the ground water where it may play an important role in europhication processes.
In the wastewater engineering field organic substances may be measured by the amount of oxygen it takes to oxidize it chemically. This amount of oxygen is referred to as the “chemical oxygen demand” (COD), which is basically a measure of organic matter content or concentration. A large fraction of COD in wastewater may be biodegradable and thus converted to sludge, which is expensive to remove and requires post-treatment. An aerobic wastewater treatment facility is essentially a “waste sludge factory”. Oxygen must continuously be supplied by aerating the wastewater at the great expense of energy to operate the aerators.
Nitrification may take place in the biological aerobic zone. Nitrification is the biological oxidation of ammonia with oxygen into Nitrite followed by the oxidation of those Nitrites into Nitrates.
A main problem addressed by the present invention is that the amount of undesired components in wastewater should be reduced in order to prevent pollution by the effluent outlet.